Jack played a psychologist patient named Elliott Carlin in nearly 50 episodes of The Bob Newhart Show for CBS. Known for his narcissistic and neurotic behavior, Jack Riley’s Elliott Carlin became a memorable and favored character on the show, which explains why the writers kept adding him into episodes throughout the show’s original run. Later in his career, Jack’s voice acting helped him to reach a much younger generation as Stu Pickles on the popular Nickelodeon cartoon Rugrats.

(Photo Credit: Kevin Winter/Getty Images)

According to the Hollywood Reporter, Riley passed away in a Los Angeles hospital. Paul Doherty from Cunningham Escott Slevin & Doherty opened up about Riley’s death to the media outlet, confirming that Jack Riley died “of pneumonia after a long illness.”

Bob Newhart paid tribute to his former co-star on Twitter Saturday, giving the recently deceased actor credit for bringing such a memorable character to life on the popular CBS sitcom.

Jack Riley “Elliot Karlin” created one of the most endearing characters on situation comedy. He shall be sorely missed.

Newhart was not the only co-star from Jack Riley’s past that honored his memory on Twitter after the news of his passing started circulating online. Two voice actors that also helped to bring the Rugrats characters to life, Tara Strong and Cree Summer, paid their respects to the longtime actor via social media as well.

Joe Alasky (Grandpa Lou’s second VA) and now Jack Riley the voice of Stu. Geez…well, looks like a Rugrats reboot is pointless now.

— Felix Anthony Saenz (@FelixASaenz) August 19, 2016

John “Jack” Riley was born in Cleveland, Ohio, in December of 1935. After being discharged from the United States Army, Jack made a name for himself in his hometown as a popular radio personality. With a little help from his friend, comedy legend Tim Conway, Jack Riley moved to Los Angeles in the 1960s and eventually wrote comedy sketches professionally. Before long, Riley transitioned his talents onto the small screen with a number of different acting opportunities.

RIP Jack Riley, who you saw as the Desk Clerk in Hitchcock spoof HIGH ANXIETY. He was RUGRATS’ Stu Pickles, too. pic.twitter.com/L1razzW83O

In addition to The Bob Newhart Show and Rugrats, Jack Riley built an impressive list of acting credits from a vast number of other popular television shows, including The Mary Tyler Moore Show, Gomer Pyle, Night Court, Hogan’s Heroes, and Diff’rent Strokes. Jack Riley frequently collaborated with Mel Brooks as well, appearing in such popular films as High Anxiety, To Be or Not to Be, and Spaceballs.

Jack Riley also appeared in such popular ’90s sitcoms as Friends, The Drew Carey Show, and Seinfeld. Jack Riley married Ginger Lawrence-Riley in May of 1975, according to People magazine. During their 41 years of marriage, Jack and Ginger had two children together.